Process for determining the operability of the structural components of the dialyzate section of a dialyzer of a hemodialysis apparatus, comprising volumetrical ultrafiltration in the dialysis liquid circuit and a control system for the ultrafiltration rate connected to a pressure transducer on the outlet of the dialyzer downstream of the associated dialyzer valve and a safety system based on monitoring of the transmembrane pressure, whereby the march of pressure (pressure as a function of time) in the dialyzer in the dialyzer liquid circuit is drawn upon when the dialyzer is in switched off state by detection of the signals of the pressure transducer to determine operability, together with the corresponding apparatus for executing this process.
Hemodialysis apparatus with volumetrical ultrafiltration (UF) control have found broad application. Appliances of this type are produced and marketed, e.g. by the applicant (hemodialysis apparatus of the Fresenius Company Series 2008 C, D, E). The UF control arrangement of these appliances permits predetermination of a specified ultrafiltration rate resp. ultrafiltration quantity. It then ensures that the predetermined ultrafiltration rate resp. quantity is withdrawn during the heamodialysis treatment, independently of the viscosity of the blood to be treated and the properties of the hemodialyzer.
It is known that such a control arrangement may lose its capacity for precise control of the ultrafiltration rate as a result of a defect.
Since, for example, a dramatic increase in the ultrafiltration rate caused by such a defect may endanger the patient, established safety standards (IEC 601 Section 16) require that a safety system must be present, which prevents an ultrafiltration dangerous to the patient. Monitoring of the transmembrane pressure (TMP) is accepted as such a safety system.
The development of dialyzers with membranes of high permeability--so-called high-flux dialyzers--has, however, resulted in the fact that, due to the limited resolution of the TMP sensor, TMP monitoring cannot determine a dangerously high or low ultrafiltration rate with sufficient resolution.
To ensure that at least the treatment starts with an intact ultrafiltration control system, arrangements have come into the market which permit manual or automatic examination of the integrity of the control system prior to treatment. This examination occurs by means of a pressure maintaining or holding test in the dialyzate section of the apparatus.
Experience has shown that technical apparatus usually becomes defective during operation and not in disconnected state.
The invention therefore proceeds from the problem of providing a process which also facilitates determination of the operability of the control system for the ultrafiltration rate during dialysis treatment by means of a pressure maintaining test, without additional devices for pressure variation.
This problem is solved, proceeding from the process specified above, in that during dialysis the dialyzer is periodically separated from the dialyzer is liquid circuit for a brief time interval respectively, during which the average dialyzate operating pressure is stable in tight state, and the march of pressure in the dialyzing liquid circuit of the separated dialyzer is monitored in the manner of a pressure maintaining test known per se for deviation from the stable state.
The process detects defective ultrafiltrations which may become dangerous in the current operating state by simple means.
To create realistic conditions, the process is usefully executed in such manner that the time interval during which the pressure maintaining test is performed typically is in the range of 20 seconds.
Since the threshold for defective ultrafiltration is reached differently in the case of error, depending on the ultrafiltration coefficient of the dialyzer used, the process is executed according to a further development of the invention in such manner that the period between two pressure maintaining test intervals is determined on the basis of the ultrafiltration coefficient of the dialyzer used in accordance with the equation EQU .DELTA.t=(.DELTA.UF/p* (60/UFC))
whereby .DELTA.t=period, .DELTA.UF=max. error of the ultrafiltration, p=transmembrane pressure and UFC=ultrafiltration coefficient (volume per unit of time and unit of pressure).
The process may be executed manually or automatically. An apparatus for automatic execution of the process is usefully characterized according to the invention in that a microprocessor system which periodically generates switching signals in predetermined intervals for separating the dialyzer from the dialyzing liquid circuit for a predetermined time interval is provided in the hemodialysis apparatus, whereby, in addition to the signal of the pressure transducer, all necessary values are fed to the microprocessor and the microprocessor generates an indicator/alarm/switch signal depending on the march of pressure during the time interval.
Further developed features of the invention as well as features concerning the determination of the operability of an arrangement of the hemodialysis apparatus connected to the ultrafiltration control arrangement are shown in the description passages relating to the exemplary embodiments shown in the drawing.